07

Energy output

A human organism does not need energy only to produce movement activity. Energy is also released during the sleep. All events taking place in the human body require energy. When issuing nutritional recommendations it is necessary to be aware of how much energy the human body gives out under resting conditions as well as during various daily routines or sports activities.

A number of units are used to measure energy. Most frequently these are joules (J), or kJ. In Northern America calorie (cal), or kcal (kilocalories) are used. In measuring of the energy output the MET unit is used, or the so called metabolic equivalent where 1 MET = 3.5 VO2 ml/min/kg.

Basal metabolism refers to the minimum energy consumption necessary to sustain basic physiological functions (about 1.200-2.400 kcal/24hours which is roughly equivalent to 5.000-10.000 kJ/24 hours).

Resting metabolism refers to energy output under resting conditions (sleep, lying position, sitting position) which is about 10% higher than of the basal metabolism.

Activity metabolism refers to energy output in various activities, whether daily routine or sports ones (Tab. 1).

The minimum energy output during a routine daily activity is about 1.800-3.000 kcal/24hours which is roughly equivalent to 7.600-12.600 kJ/24 hours. This is, however, influenced by a number of factors including sex, age, body build and overall fitness of a person in question. We are more likely to detect the increased BM values in athletes than in the non-sporting population.

The minimum energy output during a daily routine activity is about 1.800-3.000 kcal/24 hours which is roughly equivalent to 7.600-12.600 kJ/24 hours.

Table 1 Energy expenditure values for the selected activities and sports activities

kJ/hHabitual and physical activities
to 400 kJsleeping, reading, writing, PC work, watching TV, car driving
400-800 kJironing, eating and cooking, washing and hygiene, dressing, washing-up, biliard
800-1000 kJmopping floors, gardening, lite aerobic, shopping, walking (4 km/h)
1000-1500 kJsrubbing floors, vacuuming, window cleaning, table tenis, volleyball, dancing, walking (6 km/h), most recreational sports
1500-1900 kJrunning (8 km/hod), skating, sexual activity, intense aerobic, soccer, mountain hiking, swimming - breast, fitness trainig
1900-2100 kJcycling (20 km/hod), alpine skiing, tenis, canoeing, spinning, walking up stairs, chopping wood, dancing (competitive), swimming - crawl, basketball
2100-2500 kJfast running, X-country skiing, swimming (competitive), climbing, snow removal, floorball, jumping rope, squash, badminton

Energy expenditure measurement

The level of energy expenditure may be determined through direct and indirect calorimetry. Being technically and financially demanding the direct calorimetry is used very rarely. The person examined is left in a closed room from which the air is conducted away. The heat produced by the organism is measured. The indirect method is used more frequently.

The Herris-Benedict formula presents the simplest way to estimate the basal metabolism:

For females:

BMR (kcal) = 655 + (9.6 × weight in kg) + (1.8 × height in cm) - (4.7 × age in years)

For males:

BMR (kcal) = 66 + (13.7 × weight in kg) + (5 × height in cm) - (6.8 × age in years)

e.g. 50-year old woman, with the weight of 65 kg and height of 165 cm will calculate BMR using the formula in the following way:
BMR = 655 + (9.6 × 65) + (1.8 × 165) - (4.7 × 50) = 1 348 kcal = 5 640 kJ

Charts (Tab. 2, 3) are usually used to measure energy expenditure during 24 hours where individual activities are matched with the value of the basal metabolic rate (BMR) which expresses in percentage by how much an activity value is greater than the one of the basal metabolic rate (100%).

FORMULA

Table 2 Mean increase of energy expenditure in various habitual activities (adjusted according to Heller, 2005)

Habitual activity% due BMHabitual activity% due BM
Sleeping110Car driving190
Lying (awake)115Dressing210
Reading120Cooking235
Small manual work130Washing, hygiene245
Writting135Biliards260
Studying140Shopping290
Singing, speaking140Window cleaning310
Eating145Dancing450-690
PC typing160Playing with children450-910
Laboratory work180-250Gardering500

Table 3 Mean increase of energy expenditure in various physical and athletic activities (adjusted according to Heller, 2005)

Activity/Sport% due BMActivity/Sport% due BM
Walking 4 km/h290Aerobic660
Walking 5 km/h355Badminton540-790
Walking 6 km/h445Basketball1000
Walking 7 km/h520Soccer1000
Running 9 km/h860Golf350-620
Running 10 km/h950Art gymnastics620
Running 12 km/h1060Ice-hockey1000
Running 14 km/h1280Mountain hiking610
Cycling 12 km/h400Alpine skiing - recreation1000
Cycling 16 km/h580x-country skiing - recreation750
Cycling 20 km/h800Strengthening1000
Cycling - competitive1000Squash1000
Swimming 1.2 km/h330Table tenis540
Swimming 1.8 km/h530Tenis825
Swimming 3.0 km/h1000Volleyball650

The O2 measurement using an air analysator presents a more accurate method to measure energy expenditure. This method which recognizes individual differences may be used to measure both basal (resting) metabolism and energy expenditure in various movement activities. The value of the oxygen intake varies depending on the intensity of physical exercise.

Fatigue

Fatigue is a physiological state which follows after a period of physical as well as mental stress. In fact it is a defensive mechanism acting to protect our organism from a possible strain injury. Muscle fatigue results from the reduced production (resynthesis) of macroergic phosphates (ATP) accompanied by critical reduction of energy reserves or accumulated metabolites. Fatigue may be of total, local, physical, mental or acute or chronic kinds.

Viewed from the perspective of concrete metabolic changes in muscles the fast (anaerobic) fatigue and slow (aerobic) fatigue are recognized.

Acute fatigue refers to existing common fatigue felt as a direct consequence of an ongoing activity while chronic fatigue results from long-term strain where remnants of fatigue accumulate. Pathological fatigue beyond physiological dimension is often encountered too. Here we talk about the overtraining syndrome (OS).

The overtraining syndrome is characterized by reduced performance accompanied by disorders both in the area of regulation of physiological functions and the mental area.

Fully developed overtraining is not common and it needs to be differentiated from short-term overload or overreaching. Chronic condition of overtraining is characterized by excessively rising intensity of the training load, both repetitive and permanent, as well as by insufficient recovery.

The term overload refers to the planned, systematic and progressive increase of the load to achieve increase in the overall performance. Overreaching refers to repetitive acute overload without adequate recovery where the adaptive abilities of an individual are exceeded. This condition results in decreased performance spanning a few weeks or months. Both the overtraining syndrome and a subsequent recovery period usually take many more weeks or months.

Comment:
Máček, Radvanský (2011) add to the topic of over-training syndrome: "The term over-training has been abandoned in recent years because according to present opinions it does not represent the essence of the problem and has been replaced by term unexplained under-performance syndrome (UPS). The reason for this change is a distortion of causes of the pathological state using the original term, which states an inadequate increase in intensity or duration of training load as the only cause of this state, while there might be not only more causes, but also the mechanism is much more complicated."